The use of spreader bar systems for lifting tubulars is well-known in the art. Examples of such spreader bar systems include, e.g., U.S. Pat. No. 4,397,493 to Khachaturian, et al., and U.S. Pat. No. 5,603,544 to Bishop, et al. The advantage of these systems is that they allow the force of a single-point lifting system, such as a shackle or hook, to be divided into multiple lifting points, thus avoiding the material stress and safety concerns associated with lifting a heavy load by a single point.
In order to adapt the shackle and spreader bar systems for various dimensions and weights, it is common to utilize an “end cap” system (also known as a compression cap system) for attaching spreader bars to the shackle. In this system, the spreader bar is fitted between two “end caps,” which contain multiple orifices for connecting to both the lifting mechanism above and the load below. This allows for quick swapping of various sizes and weights of spreader bar as necessitated by the lift.
However, there are still several drawbacks to the state of the art in spreader bar lifting. Assembly of the end cap requires precise alignment of the end cap with the spreader bar, and often requires a tubular spreader bar to be physically altered (e.g., through spot welds or attachment holes) which can weaken the spreader bar's tolerance for metallurgical stresses.
Additionally, the process of determining the correct end cap fitting for use with a given load and span of weight to be lifted can often be time-consuming and prone to error when calculated by workers in the field. This can lead to an increased stress on the equipment and the risk of lift failure.
A need therefore exists for an end cap system in which both the method of selecting a properly rated and sized end cap and the physical method of fixing the end cap to a selected spreader bar are simplified to allow field personnel to more quickly and reliably rig-up lifting systems. Embodiments disclosed in the present invention meet these needs.
One or more embodiments are described below with reference to the above-listed Figures.